[orbital-decay]

Regardless of encryption or authorities cooperation shenanigans, Telegram has (had?) a serious privacy issue in that your number is public by default, and even if you set it to private after the registration, it gives enough time for a state actor to siphon your phone number off your profile, by running a bot with access to SMS. Which is enough for all practical purposes.

The only real reason ex-Soviet drug users keep using Telegram is they are careless and it's popular. Another suspicion of many is that most of the drug trade in Russia is under FSB "protection", and they have no reason to kill the goose that lays golden eggs. Drug dealers only run Telegram for their clientele though, with anonymous SIMs and Tor; for more serious purposes, they and other criminals use more secure communication channels, XMPP in particular.

>the Telegram's owner (Pavel Durov) relocated from Russia for ever due to issues with his previous project (VK)

...while keeping Telegram developers in Moscow and regularly showing up there himself. (no idea whether it's still true, probably not)

I can't say with 100% confidence that Telegram itself is compromised, though, there's no clear evidence for that. Some smoke probably, but no fire, sketchy indeed.